1. Technical Field
The present invention relates in general to an improved thermal management design and, in particular, to an improved system, method, and apparatus for thermally bypassing selected components in electronic equipment.
2. Description of the Related Art
It is well known in the industry that heat contributes to early failures of electronic equipment. As processor clock speeds and rotational speeds of magnetic media increase and the number of processors used in some systems (e.g., servers) increases, heat becomes even more of an issue. In some designs it is necessary to use air that has already passed over hot components to cool other components that are further “downstream” with respect to the airflow.
For example, in IBM's BladeCenter™, air enters a frontal enclosure, passes numerous server blades, then passes through network switch modules, management modules, and power modules before finally being drawn out of the system and expelled from the enclosure via blowers. Thus, the ambient air is heated (e.g., to as much as approximately 54° C.) by the upstream components located at the front of the enclosure before arriving at the subsystems in the rear of the enclosure.
FIG. 1 depicts an enclosure that is similar in many regards to the BladeCenter™ system enclosure 100. The system enclosure 100 comprises one or more server blades 110 (which, in turn, comprise one or more CPUs, memory, support and I/O chips, DASD, etc.), one or more network switch modules 130, and one or more air moving devices 150 (e.g., a fan or blower). Also within the enclosure 100 are a number of air plenums, such as a central plenum 120 and a plenum 140 at the entrance to the air-moving devices 150.
Air 160 enters the front of the system enclosure 100 and passes across the server blade components 110 where it is “pre-heated” 160a by those components 110. The heated air may diverge along different paths with some air 160b traveling to the top of the enclosure 100 and passing down through the network switch modules 130 or other components where it is further heated 160d. Some air 160c may traverse other routes to reach the final plenum. The mixture of all of the heated air is then expelled 160e from the system enclosure 100.
The use of “pre-heated” airflow in system enclosures results from two requirements. First, some applications mandate only front-to-rear airflow within the enclosure, since there are constraints on the use of the top, bottom, and sides of the enclosure for cooling purposes. Second, these configurations minimize server volume and the paths provided for airflow. Thus, the continued or reuse of air through “series cooling” of devices is essential.
In the prior art, a number of solutions have been proposed to address this issue. For example, in U.S. Pat. No. 4,935,864, a Peltier device is bonded to an integrated circuit chip. The cold side of the Peltier device cools the chip and the hot side is connected to heat sinks to dissipate heat. This design uses a single heat exchanger and requires a redesign of the subsystem to incorporate the Peltier device and heat sink.
U.S. Pat. No. 5,431,021, teaches that the operational efficiency of a thermoelectric cooling (TEC) device can be increased by injecting moisture into the gas flowing over the hot side heat exchanger. A TEC module is a solid state device that takes advantage of the Peltier effect whereby current flowing through a junction of dissimilar metals (or of a metal and a semiconductor) produces localized heating or cooling, depending upon the direction of the current flow. TECs are configured to use hundreds of such junctions. The junctions are configured to be electrically in series and thermally in parallel, with the net effect of producing cooling on one side of the TEC and heating on the opposing side of the TEC. The history and a tutorial on TECs can be found on the Internet at, for example, www.tellurex.com/cthermo.html.
TECs also find use in applications where the cold surface is placed on one side of a thermal barrier (e.g., inside a cooler), and the hot surface is placed outside the barrier. The cold surface decreases the temperature of the air that flows around it on one side of the barrier while the air circulating on the other side of the barrier carries off heat produced by the hot surface.
The U.S. Pat. No. 5,431,021 patent describes two heat exchangers with an interposing TEC. The flow over the two heat exchangers are described as separate, possibly even different types of fluids, although it is mentioned that they might both be air. This design seeks to increase the efficiency of a TEC used in a medical device, but makes no reference to bypassing heat around a subsystem of electrical equipment.
U.S. Pat. No. 6,198,628, teaches a method of providing localized cooling within an enclosure: a serial airflow is provided from some inlet vents, through a number of subsystems, through an air moving device, and out of the enclosure. In addition, one or more parallel air paths are provided to allow air to enter through alternate inlets and pass directly over subsystems where localized cooling is required before joining the serial airflow stream and passing thought he air moving device and out of the enclosure.
Another way hotter subsystems have been handled was to increase the flow of air through the enclosure. However, there are practical constraints on how fast and how much-air can be blown through an enclosure. In addition, increased airflow rates give rise to other problems such as increased noise and increased contamination (e.g., dust and lint) as large volumes of ambient air are drawn into the enclosure and “filtered” by the internal components.
As processors continue to increase in speed and power consumption, there is also a point of diminishing returns. Eventually, either the downstream components must acceptably cooled by hotter air, or the ability to support the same number of upstream components must be restricted to reduce pre-heating. It would be desirable to allow higher levels of pre-heating by some components without affecting the intake temperature of downstream components.